Abstract In Magnolia Field, deepwater sediments were affected during deposition by allochthonous salt. Pleistocene channel systems developed on a salt flank and were initially deeply incised close to the salt but progressively avulsed down the lateral slope, each time with decreasing depth of incision. Following this degradational stage, a lobe developed on top of the channel fills and a large-scale aggradational system developed. A conceptual model of submarine channel development adjacent to active topography has been developed from this dataset. Channels may become deeply entrenched during stages of salt growth, but only where flow frequency and magnitude are sufficient to outpace topographic growth. Where flows are less frequent topographic growth may present a barrier to successive flows, causing avulsion. The large-scale cycles of salt growth and withdrawal commonly recognized in subsurface systems, combined with eustatic sea-level changes, may result in a cyclic style of evolution whereby channels initially become entrenched and/or step away from the growing topography, switching to backfilling as salt growth slows or pauses, followed by a distributive-style as the entire system backsteps. During salt withdrawal the equilibrium profile may become relatively raised and channels may develop an aggradational style. In these settings, significant cross-channel facies asymmetry may result.

Abstract The late Mesozoic to early Tertiary Magallanes foreland basin in southernmost Chile formed when regional shortening related to the Andean orogeny caused the inversion of the earlier Rocas Verdes back-arc basin into a retroarc foreland basin during the Late Jurassic. This inversion, the orogeny, and the onset of deep-water sedimentation is recorded by the ~1000 m thick Punta Barrosa Formation (Turonian-Coniacian), characterized by 40-150 cm thick, generally medium-grained, tabular, turbiditic sandstone beds that alternate with abundant shale, sandy slurry flow and debris flow deposits. Sedimentation style changed during deposition of the overlying Cerro Toro Formation (Coniacian-Campanian), which consists of thick successions of thin-bedded mudstone and sandstone turbidites and debris flow deposits interrupted by thick (up to 400 m) deep-water channel complexes. The channels are filled with conglomeratic turbidity current deposits, conglomeratic slurry flow deposits, and thick-bedded turbidite sandstone. Sediment transport was dominated by a 5-8 km wide axial channel belt with southward directed paleocurrents. Potential tributary channel complexes, possibly confined behind a local structural high, seem to have funneled sediment into the axial channel. In contrast, the overlying Tres Pasos Formation (Campanian) comprises marine slope deposits that represent southward progradation into the basin. The transition from slope deposits into shallow-marine sediments is recorded by the Dorotea Formation. The Magallanes Basin remained a site of deep-water sedimentation for at least 15 m.y., from the Turonian through the Campanian. The sedimentation style of the deep-water basin fill varied significantly throughout the three formations and the basin fill eventually shoaled upward into shallow-marine and deltaic deposits. The sculpting of the outcrops by recent glaciation provides superb exposure of the basin fill, making the Magallanes Basin an excellent field area to study deep-water depositional processes as well as foreland basin evolution.